Cell Division

An informative presentation by your wacky science teacher!

LG4: Understand cells’ role in living things and heredity.

A Question…..What do you,

an ant,

and an oak tree have in common

(talk to a partner)?

An Answer….

Yes, you are all living things…but more importantly

You are all made of trillions of cells!

AND

you all started out as a single cell!

Cell Theory

In the 1830’sTheodor

Schwann & Matthias Schleiden

proposed “Cell Theory”

Cell Theory states…

1. All living things are made of cells.

2. Cells are the basic unit and function of all living things.

3. Living cells only come from other living cells.

CellDivision…

Through cell division, a single cell becomes two cells. Those two cells divide into four….

Time for math… how many cells would you have after 6 divisions?

Zygote

How do you become a multicellular organism if you started out as just ONE cell (talk to a partner)?

How Many?

You would have 64

cells!

That’s a

lot of

cells!

Cell Division Cells multiply by dividing!Answer (talk to your neighbor):• How does your drawing show

that cell division can cause organisms to grow larger in size?

• Is there a limit to how large a cell can be? Why or why not?

Consider….

What are the purposes of cell division?

Regrowth/growthRepairReproduction

(Hint: This is important!)

Regrowth/Growth

How tall were you when you were 5?

How tall were you last year?

How tall are you now?

Do you think: Your cells got bigger?

or

Your cells divided to produce more cells?

(talk with a neighbor)

Regrowth While individuals grow in size, a larger organism has

MORE CELLS than a smaller organism

There are limits on how big a cell can get. What do you

think is the main reason why cells only get to be a

certain size?

RegrowthCells continue to divide to help an organism or part of an

organism grow

As the cell grows, more processes are needed for it to function, so its demand for instructions increases. However, the amount DNA (instructions) remains constant. The instructions will determine what type of cell it becomes.

Specialization

We know that cells divide in order to make bigger organisms. However, if cell division

were the only process occurring in cells, all multicellular organisms would end up

as spheres of identical cells.

During development, cells become specialized to perform particular functions.

In Other Words….

Cells get instructions from DNA about what type of cell it will become and

what will be its function!

Cell TypesSome cells might

become layered skin cells, while

others might become long,

thin nerve cells. Nerve Cells

Cheek Cells

Bone CellsRed Blood Cells

One purpose of cell division

Regrowth

Next reason…

Repair

Have you gotten a paper cut recently?

Have you broken a bone in your arm

or leg?

Repair

The body repairs injuries like these by means of cell division. For example…….

When your skin is cut, skin cells on either side of the cut make new cells to heal the wound.

Repair As cells age and die, they need

to be replaced.

In the human body:

-There are about 200 different types of cells (remember the pictures?).

-Every minute or so, your skin loses about 40,000 cells!

-In contrast, your brain cells live a very long time!

Regrowth

Next reason…

One purpose of cell division

Reproduction

In order for organisms to reproduce, reproduction (sex cells – meiosis) must occur

Reproductive cell division produces sex cells

with ½ the genetic information from each parent (humans – 23 from mom / 23 from dad)

Summary…

Cells are the main components of all living things

The purpose for cell division: Regrowth Repair Reproduction

Cell Cycle

Mitosis in Words

The Cell Cycle

Cell grows, makes a copy of DNA.(90% of cell’s life is spent here!)

Chromosomes and spindle fibers form; nuclear envelope breaks down.

Chromosomes line up across the center and attach to a spindle fiber.

Centromeres split; chromatids separate and move to opposite ends.

Chromosomes stretch out; new nuclear envelope forms around chromosomes.

Cell membrane pinches in two; each daughter cell has same number of identical chromosomes.

Interphase

ProphaseCytokinesis

Telophase

Anaphase

Metaphase

Length of the Cell Cycle

Mitosis

One More Look at Mitosis

Meiosis (“my-o-my! Sex Cells!)

The process by which the number of chromosomes is reduced by half to form sex cells (sperm and egg)

Chromosome pairs separate and are distributed to two different cells. The resulting sex cells have only half as many

chromosomes as the other cells in the organism.

Meiosis Requires two

divisions of the nucleus Meiosis I- (Just

like mitosis) Meiosis II- two

daughter cells go through a second division of the nucleus. (during this process, there is no chromosome replication)

Meiosis II (after Meiosis I which is Mitosis)

 

The difference between Mitosis and Meiosis

(W.U. - copy this slide into notes)Mi”T”osis

(“T” is for TWIN!)

Meiosis

(“MY-OH-MY! SEX CELLS!)•One division of the nucleus = 2 cells

•Used for growth and repair•Creates exact “T”win of cell (diploid cells)

•Two divisions of the nucleus

(mitosis, THEN meosis = 4 sex cells cells)

•Used for sexual reproduction

•Creates cells with ½ genetic material (haploid cells) – in humans, 23 chromosomes from each parent = new human with 46

•Cancer is Uncontrolled Mitosis:

Mitosis must be controlled, otherwise growth will occur without limit (cancer)

•Mutations in control proteins can cause cancer

Cancer is a disease in which cells grow and divide uncontrollably, damaging the parts of the body around them. It is caused by a mutation that causes uncontrolled mitosis.

Cancer Cells – What is it?

Cancer cells are held together.

Mutations

A mutation (from Latin word that means change) is any change in a gene or chromosome.

Can cause a cell to produce an incorrect protein during protein synthesis.

As a result, the organism’s trait, or phenotype, may be different from what it normally would have been.

Results of Mutations

If a mutation occurs in a SEX CELL, the mutation can be passed on to an offspring and affect the offspring’s phenotype.

If a mutation occurs in a BODY CELL, the mutation will not be passed on to the organism’s offspring.

Effects of mutations

Introduce change in an organism (genetic variation)

Can be harmful (reduces the organism’s chance for survival and reproduction)

Can be helpful (improve an organism’s chance of survival and reproduction)

Antibiotic resistance in bacteria Can be neither harmful nor helpful

Rate Yourself!LG4: Understand cells’ role in living things

and heredity.

“Before this presentation, I was a _____ (scale rating 0-4)

because I knew __________ about cells.now, I feel like I am a _____ (scale rating 0-4) because I learned

Don’t forget to thank a science teacher today!